This invention relates to a photoelectric conversion device and a photoelectric cell comprising the same. More particularly, it relates to a photoelectric conversion device using dye-sensitized semiconductor particles and a photoelectric cell comprising the device.
In the field of photovoltaic power generation, the focus of research and development and practical application has been chiefly put on monocrystalline silicon solar cells, polycrystalline silicon solar cells, amorphous silicon solar cells, and compound solar cells using cadmium telluride, copper indium selenide, etc. It is required for spread of solar cells to overcome such difficulties as a high production cost, a short supply of raw materials, and a long energy payback time. Although many solar cells using organic materials have been proposed aiming at an increase of working area and a reduction of cost, they have a low conversion efficiency and poor durability.
Under these circumstances, Nature, vol. 353, pp. 737-740 (1991) and U.S. Pat. No. 4,927,721 disclose a photoelectric conversion device using dye-sensitized semiconductor particles, a solar cell comprising the device, and materials and techniques for producing them. The proposed cell is a wet type solar cell comprising, as a work electrode, a porous thin film of titanium dioxide spectrally sensitized by a ruthenium complex. A primary advantage of this system is that such an inexpensive oxide semiconductor as titanium dioxide can be used without being highly purified so that a photoelectric conversion device can be supplied at a competitive price. A secondary advantage is that the sensitizing dye used shows a broad absorption spectrum so that substantially the whole range of visible light can be utilized.
For practical use as a solar cell, it is required for the porous thin film of semiconductor particles such as titanium dioxide to have a roughness factor of about 1000 so as to secure a large specific surface area. For this purpose, fine pores on the order of nanometer (a nano-porous structure) should be made. Methods for forming a porous thin film of titanium dioxide are described, e.g., in Masao Kaneko (ed.), Hikari Energy Henkan -Kiso to Ohyo-, ch. 3, xc2xa7 2, IPC K.K.
In order to form a nano-porous thin film, wet processes comprising applying a dispersion or a colloidal solution of semiconductor particles onto an electrically conductive substrate are preferred to dry processes, such as vacuum deposition, which are unsuited to large-scale production and costly. A dispersion or a colloidal solution of the semiconductor particles to be used in the wet processes can be prepared by a sol-gel process, a method comprising grinding a semiconductor in a mortar, or a method comprising wet grinding a semiconductor in a mill. A synthetic semiconductor as precipitated in a solvent in the form of fine particles can also be used as such. However, a sol-gel process needs high temperature for converting a metal hydroxide compound produced by hydrolysis into an oxide. In addition, a conventional sol-gel process has difficulty in obtaining monodisperse particles, meeting difficulty in forming a uniform nano-porous film. Further, the particles ground in a mortar or dispersively ground in a mill are liable to agglomerate, making it difficult to establish the conditions for obtaining a nano-porous film.
The difficulty in forming a nano-porous semiconductor layer suitable for use in a photoelectric conversion device and a photoelectric cell has been a bar to improvement in short circuit current and photoelectric conversion.
An object of the present invention is to provide a dye-sensitized photoelectric conversion device and a photoelectric cell having a high short circuit current and a high photoelectric conversion.
Other objects and effects of the present invention will become more apparent from the following description.
The above objects of the invention have been achieved by providing the following photoelectric conversion devices and photoelectric cell.
(1) A photoelectric conversion device having a photosensitive layer comprising semiconductor particles obtained from a metal hydroxide gel or a precursor thereof present in a hydrophilic solvent.
(2) The photoelectric conversion device according to the above item (1), wherein said metal hydroxide gel or said precursor is formed by hydrolysis of a stable metal complex.
(3) The photoelectric conversion device according to the above item (2), wherein said metal complex has a ligand selected from the group consisting of compounds having a hydroxyl group, a carbonyl group, an ester group or a carboxyl group and amine compounds.
(4) The photoelectric conversion device according to the above item (2) or (3), wherein said metal complex has a multidentate ligand.
(5) The photoelectric conversion device according to any one of the above items (1) to (4), wherein said semiconductor is a metal chalcogenide.
(6) The photoelectric conversion device according to any one of the above items (1) to (5), wherein said semiconductor comprises at least one chalcogenide compound of a metal selected from the group consisting of titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium and tantalum.
(7) The photoelectric conversion device according to any one of the above items (1) to (6), wherein said semiconductor is a metal oxide.
(8) The photoelectric conversion device according to any one of the above items (1) to (7), wherein said semiconductor is titanium dioxide.
(9) The photoelectric conversion device according to any one of the above items (1) to (8), wherein said semiconductor particles have a coefficient of particle size variation of 30% or less.
(10) The photoelectric conversion device according to any one of the above items (1) to (8), wherein said semiconductor particles have a coefficient of particle size variation of 20% or less.
(11) The photoelectric conversion device according to any one of the above items (1) to (10), wherein said semiconductor particles are sensitized with a dye.
(12) The photoelectric conversion device according to the above item (11), wherein the dye is at least one of a ruthenium complex dye and a methine dye.
(13) The photoelectric conversion device according to any one of the above items (1) to (12), further having a charge transporting layer comprising a molten salt electrolyte.
(14) The photoelectric conversion device according to any one of the above items (1) to (12), further having a charge transporting layer comprising a hole-transporting material.
(15) A photoelectric cell comprising a photoelectric conversion device according to any one of the above items (1) to (14).